700 



REPRODUCTION. 



FIG. 251. 



Diagram of the CIRCULATION THROUGH 

 *THE FCETAL HEART. . Superior vena 

 cava. b. Inferior vena cava. c, c, c, c. 

 Arch of the aorta and its branches. 

 d. Pulmonary artery. 



thoracic aorta ; while the blood of the inferior vena cava, entering the 

 left auricle and left ventricle, passes into the arch of the aorta, and is 

 distributed to the head and upper limbs. The two streams, therefore, 



in passing through the heart, cross each 

 other both behind and in front. The 

 venous blood, returning from the head 

 and upper limbs by the superior vena 

 cava, passes, through the thoracic and 

 abdominal aorta and the umbilical ar- 

 teries, to the lower part of the body, 

 and to the placenta ; while that return- 

 ing from the placenta, by the inferior 

 vena cava, is distributed to the head 

 and upper limbs, through the vessels 

 given off from the arch o/ the aorta. 



This division of the streams of blood, 

 during a certain period of foetal life, is 

 so complete that Reid,* on injecting the 

 inferior vena cava with red, and the 

 superior with yellow, in a human foetus 

 of seven months, found that the red 

 injection had passed through the foramen ovale into the left auricle 

 and ventricle and the arch of the aorta, and had filled the vessels of 

 the head and upper limbs ; while the yellow had passed into the righl? 

 ventricle, pulmonary artery, ductus arteriosus, and thoracic aorta, with 

 only a slight admixture of red at the posterior part of the right auricle. 

 All the branches of the thoracic and abdominal aorta were filled with 

 yellow, while the whole of the red had passed to the upper part of 

 the body. 



We have several times repeated this experiment on the foetal pig, 

 when about one-half or three-quarters grown, first washing out the 

 heart and large vessels with a watery injection, to prevent their obstruc- 

 tion by coagulated blood. The injections used were blue for the supe- 

 rior vena cava, and yellow for the inferior. The two syringes were 

 managed, at the same time, by the right and left hands ; their nozzles 

 being held in place by an assistant. When the points of the syringes 

 were introduced into the veins at equal distances from the heart, and 

 the two injections made with equal rapidity, it was found that at least 

 nineteen-twentieths of the yellow injection had passed into the left 

 auricle, and nineteen-twentieths of the blue into the right. The pul- 

 monary artery and ductus arteriosus contained a similar proportion of 

 blue, and the arch of the aorta of yellow. In the thoracic aorta, how- 

 ever, there was always an admixture of the two colors, generally in 

 about equal proportions. This may be owing to the smaller size of the 



* Edinburgh Medical and Surgical Journal, 1835, vol. xliii., p. 11. 



